1. Field of the Invention
This invention relates to a photoresist composition. More particularly, this invention relates to an alkali-developable positive photoresist composition suited for photofabrication such as bump formation, wiring, interlayer insulating film formation, circuit protective film formation and processing and manufacture of precision parts, carried out when circuit substrates are manufactured and semiconductors and electronic parts are packaged on the circuit substrates.
2. Description of the Prior Art
The photofabrication is a generic term for techniques in which a photosensitive resin composition is coated on the surfaces of process articles and the coating films formed are patterned by photolithography, followed by chemical etching or electrolytic etching using the patterns as masks, or electroforming chiefly using electroplating, any of which are applied alone or in combination, to fabricate various precision parts. This is prevalent in the current precision fine processing techniques.
In recent years, with the downsizing of electronic equipment, there are a rapid progress toward higher integration of LSIs and toward ASIC (application specific integrated circuits), and a demand for multipin thin-film packaging for mounting LSIs on electronic equipment, where the bare chip packaging carried out by the TAB system or flip-chip system has attracted notice. In such multipin packaging, protruded electrodes of 20 .mu.m or more in height, called bumps serving as connecting terminals, must be arranged on the substrate in a high precision, and it has become more required to make the bumps higher in precision so as to be adaptable to any further miniaturization of LSIs in future.
As materials for bump formation used when such bumps are formed, thick-film resists are used. The thick-film resists are meant by resists that can form films of at least about 20 .mu.m thick on substrates. As requirements for such thick-film positive resists, it is needed that they can form films of at least 20 .mu.m thick, have an adhesion to the substrates, have a plating solution resistance and a good wettability to plating solutions when plated to form bumps, and can be readily stripped with stripping solutions.
On the other hand, conventional positive resists for pump formation can not be satisfactory in view of the adhesion to substrates at the time of development in photolithography and also in view of the plating solution resistance. As the patterns for forming bumps are made finer in size, resists having a poor adhesion to substrates at the time of development may more cause a problem that resist patterns come off the substrates at the time of development. Also, resists having a poor plating solution resistance may cause a problem that resist patterns are deformed or cracked when immersed in plating solutions, see "HYOMEN GIJUTU (Surface Techniques) Vol.46, No.9, pp.775-777, 1995".